It has previously been proposed in U.S. Pat. No. 3,936,665 of Donoghue, issued Feb. 3, 1976, to provide an automatic computer operated control system for a papermaking machine including a plurality of sensors spaced laterally across the width of the paper sheet to provide a more uniform width characteristic in the paper sheet by adjusting the paper stock valve in the head box of such papermaking machine. U.S. Pat. No. 5,300, 193 of Rule et al., issued Apr. 5, 1994, discloses a method for controlling the paper machine stock pond consistency at the top forming roll by adjusting the vacuum pressure of a suction box in response to control signals produced by a sensor of the mass flow rate of the stock pond positioned between the forming roll and the suction box. However, unlike the present invention, this automatic control system does not employ a computer control system for adjusting a plurality of variable dewatering devices having moveable elements which engage the conveyor for the paper sheet to vary their water removal rate in response to sensors of the paper sheet characteristics spaced longitudinally along the path of the paper sheet at positions downstream from the dewatering elements.
U.S. Pat. No. 4,443,298 of Thorp, issued Apr. 17, 1984, shows a papermaking machine having hydrofoil blades and an automatic control for adjusting the width of the slot between adjacent hydrofoil blades to control the turbulence of the paper stock liquid adjacent the head box. Light sensors including light emitters which transmit light beams across the width of the paper stock to light detectors on the other side of the paper stock are used to sense the turbulence of the paper stock produced by the hydrofoil blades. The present computer control system adjusts dewatering elements to vary their water removal rate in response to the paper sheet sensor output signals in order to produce a paper sheet of improved characteristics. Unlike the present invention, this patent does not show an automatic control system for a papermaking machine including a plurality of paper sheet characteristic sensors which are spaced along the path of the paper sheet downstream from the dewatering elements. Instead, this patent is concerned with controlling the intensity or force of the turbulence of the paper stock or furnish prior to formation of the paper sheet by adjusting the position of the hydrofoil blades immediately adjacent the head box.
U.S. Pat. No. 5,421,961 of Miller, issued Jun. 6, 1995, shows a computer control system for adjusting the position of a forming board to a parallel position adjacent the output of the head box of a papermaking machine. The control system senses the position of the forming board with a transducer which detects the movement of a magnet attached to the forming board. Thus, unlike the control system of the present invention, this patent does not employ sensors spaced along the path of the paper sheet to sense the characteristics of the paper sheet and apply output signals to cause the control system to produce control signals which adjust dewatering elements in the papermaking machine for controlling the water removal rate and thereby changing the paper sheet characteristic being sensed.
U.S. Pat. No. 4,278,497 of Mellen, issued Jul. 14, 1981, U.S. Pat. No. 4,280,869 of Eckerdt, issued Jul. 28, 1981, and U.S. Pat. No. 5,169,500 of Mejdell, issued Dec. 8, 1992 all show paper sheet dewatering elements which are adjusted to vary the width between adjacent blades which contact the underside of the conveyor carrying the paper sheet or to adjust the angle of a foil contacting the underside of the conveyor to control the water removal rate of the dewatering element. However, these dewatering elements are not automatically controlled by control systems including sensors which sense the paper sheet characteristics being measured, but instead are controlled by sensors which sense the vacuum produced in a suction box having the adjustable dewatering device mounted thereon or by manual adjustment of the foil angle.